Standard microelectromechanical systems (MEMS) processing techniques create structures that are symmetric in the z axis (out of the wafer's surface) but can vary in the x and y axes (in the plane of the wafer's surface). Presently, creating asymmetry in the z-axis can be performed by deflecting with stiction plates or by selective thinning. Deflecting with stiction plates leads to devices which are sensitive to z motion, but is not easily implemented for multiple z-offsets in both the positive and negative z directions and also requires more steps and additional processing layers, thereby costing more money. Selective thinning is performed by thinning one set of teeth of a comb drive in the Z-direction, but this requires an extra mask and additional etches, and it is also rather inaccurate. One method of more easily creating asymmetry requires a top and a bottom cover enclosing the mechanism layer of the MEMS device to produce asymmetry in the negative and positive z directions. Some uses for MEMS devices require an exposed mechanism layer, and a top cover is incompatible with these uses.
Thus, there exists a need for methods to easily form z-offsets in MEMS devices without completely enclosing the MEMS device.